Method for the high-resolution evaluation of signals for one- or two-dimensional directional or frequency estimation.
The invention relates to a method for the high-resolution evaluation and, if appropriate, for the recovery of received narrow-band signals for one- or two-dimensional directional estimation. The invention also relates to a method for the high-resolution evaluation of superimposed, non-attenuated harmonic signals for one- or two-dimensional frequency estimation in the case, if appropriate, of multi-channel observations.
One- or two-dimensional methods for evaluating the direction of incidence of the different signals are known from R. Roy and T. Kailath, "ESPRIT--Estimation of signal parameters via rotational invariance techniques", IEEE Trans. Acoust., Speech, Signal Processing, vol. ASSP-37, pp. 984-995, July 1989 and A. L. Swindlehurst and T. Kailath, "Azimuth/elevation direction finding using regular array geometrics", IEEE Trans. Aerospace and Electronic Systems, Vol. 29, pp. 145-156, January 1993.
Methods for one-dimensional or two-dimensional frequency estimation in the case of single-channel observations are known from R. Roy, A. Paulraj and T. Kailath, ESPRIT--A subspace rotation approach to estimation of parameters of cisoids in noise", IEEE Trans. Acoustics, Speech, Signal Processing, Vol. ASSP-34, p.1340-1342, October 1986 and M. P. Pepsin and M. P. Clark, "On the performance of several 2-D harmonic retrieval techniques" in Proc. 28th Asilomar Conference on Signals, Systems and Computers", Pacific Grove, Calif., November 1994.
Because of their simplicity and their power of resolution, the methods, known as ESPRIT methods, for signal parameter estimation by techniques based on displacement invariances (denoted below as Standard ESPRIT methods) are suitable for directional or frequency estimation. In the case of directional estimation, displacement invariances signify the geometrical displacement of identical sensor subgroups, and in the case of frequency estimation the time-referred displacement of the equidistant sample value divided into subgroups. However, complex calculations involving a relatively high outlay on computation are generally required in the Standard ESPRIT method. Again, with rising correlation between the signals, the standard ESPRIT method loses in accuracy and cannot cope in the case of coherent signals. In the case of two-dimensional directional evaluation, all known methods for the high-resolution directionally sensitive evaluation of signals require optimization or search strategies which are expensive in terms of computing time for the purpose of assigning the signals the spatial coordinates determined in the two dimensions. Furthermore, the reliability of the known methods cannot be estimated, and thus no automatic improvement in the recording of measured values can be instituted in the presence of unsatisfactory reliability.
Directional evaluation is opening up a new field of application for itself with mobile radio or methods resembling mobile radio. When being propagated in a propagation medium, signals are subject to interference owing to noise. Owing to instances of diffraction and reflection, signal components traverse different propagation paths and overlap one another at the receiver, and lead to their extinction effects. Furthermore, instances of overlapping of the signals occur in the case of a plurality of signal sources. Among other methods, frequency division multiplex and time division multiplex methods or a method known as code division multiplex serve the purpose of facilitating the distinguishing of signal sources and thus of evaluating the signals.